Implantable medical devices for producing a therapeutic result in a patient are well known. Examples of such implantable medical devices include implantable drug infusion pumps, implantable neurostimulators, implantable cardioverters, implantable cardiac pacemakers, implantable defibrillators and cochlear implants. Some of these devices, if not all, and other devices either provide an electrical output or otherwise contain electrical circuitry to perform their intended function.
It is common for implantable medical devices, including implantable medical devices providing an electrical therapeutic output, to utilize transcutaneous telemetry to transfer information to and from the implanted medical device. Information typically transferred to an implanted medical device includes transferring instructions or programs to the implanted medical device from an external device such as an external programmer. Information typically transferred from an implanted medical includes information regarding the status and/or performance of the implanted medical device.
Existing implantable medical devices and/or external programmers, such as typical neurological stimulators, can not receive telemetry when the implanted medical device is providing therapy. The noise generated by creating electrical stimulation therapy pulses and the pulses themselves can be coupled onto the telemetry receiving antenna and the resulting noise can prevent the telemetry signal from being received. In implantable stimulators such as the Itrel 3™ stimulator, Synergy™ stimulator, and Kinetra™ stimulator manufactured by Medtronic, Inc., Minneapolis, Minn., the telemetry receiver is turned on briefly between electrical stimulation pulses. If the telemetry receiver detects any signal on its antenna between stimulation pulses, the telemetry receiver turns off the stimulation pulses momentarily in order to quiet the system to receive the downlink. After the telemetry signal is received, processed, and the resulting uplink response is sent via telemetry, the electrical stimulation pulses can then be turned on again. The window that looks for telemetry occurs every 2 milliseconds with a window width of about 220 microseconds. A wake-up burst that is at least 2 milliseconds long is then sent so that the 175 kiloHertz signal would be received by at least one of the reception windows.
A disadvantage of this technique is that electrical stimulation therapy might need to be stopped to allow for telemetry communication. If the telemetry communication duration is long (such as receiving large blocks of data from the device or downloading a new application into the implanted medical device), electrical stimulation therapy might be disabled for long periods and the side effects of not having electrical stimulation therapy enabled could impact the patient, e.g., a tremor could return for a tremor patient, pain could return for a pain patient, etc.
A technique used in implantable medical devices used in cardiac pacing is to interleave the telemetry data between electrical stimulation therapy pulses. Alternatively, pacing systems also attempt telemetry during therapy and, if the communication is unsuccessful, the system can retry the communication at a later time. Both of these methods can work well for cardiac pacing therapy, where the pulse rate of the electrical stimulation therapy is less than 2 Hertz. However, in typical neurostimulators, a pulse rate of 260 Hertz or higher for electrical stimulation therapy, so interleaving telemetry data or retrying when the electrical stimulation therapy corrupts data communication becomes impractical, as the data rate is greatly diminished.